1. Field of the Invention
The present invention relates to a navigation system having a plurality of displays for displaying, for example, output images of a navigation system, output images of a television system, and output texts of a multiplex FM (frequency modulated) character broadcasting.
2. Description of the Prior Art
FIG. 6 is a plan view of a vehicle 101, in which a plurality of displays are installed. Reference numeral 102 denotes a first display installed at a position where the driver of the vehicle cannot see it, for example, it is installed at a position where only the passengers sitting on the back seat can see it, as shown in this figure. Reference numeral 103 denotes a second display installed at a position where the driver of the vehicle can see it, for example, it is installed in a dash-board of the vehicle, as shown in the figure.
FIG. 7 is a block diagram of a navigation system having the first and second displays 102 and 103 for displaying image information. The system includes a control device (calculator) 104, for example, a CPU, connected with a GPS receiver 105 for receiving signals from satellites, a map data memory 106 storing geographical information data, an input device 107 for inputting necessary data, a gyro-sensor 108 for detecting the moving direction of the vehicle, and a velocity sensor 109 for detecting the velocity of the vehicle.
Output terminals of the control device 104 are connected with a first VRAM 110 and a second VRAM 112, for storing the data calculated in the control device 104. The first VRAM 110 is connected with the first display 102 through an output buffer 111. The second VRAM 112 is connected with the second display 103 through an output buffer 113.
The function of this system is explained below.
The driver of the vehicle inputs data regarding a destination into the control device 104, using the input device 107. The control device calculates the present position on the basis of the signals obtained through the GPS receiver 105, or on the basis of the outputs signals of the gyro-sensor 108 and/or of the velocity sensor 109. The control device searches a route to the destination position, referring to data read from the map data memory 106. The obtained data regarding the route is stored in the first and second VRAMs 110 and 112. Then the route is displayed on the first and second displays through the output buffers 111 and 113.
Command indications 102a 103a, such as a menu, a screen changing command indication, a destination position setting command indication, a surrounding facilities information getting (acquisition) command indication, a selection command indication for selecting a function of the multiplex FM character broadcasting are displayed at a part of the screen of the first and second displays 102 and 103. Using these command indications 102a, 103a, the control device can be controlled so that the data to be displayed in each screen can be changed.
When a vehicle is moving, it is required that the data to be displayed in the second display 103, which is installed at a position where the driver can see it, cannot or must not be changed from a point of view of the safety of driving. A passenger other than the driver may want to change the data to be displayed in the first display, while the vehicle is moving. However, a change of the data to be displayed in the first display 102 by a passenger other than the driver causes no problem in driving safety. Thus, a general prohibition in changing data to be displayed in both of the displays while the vehicle is moving is not reasonable. Under such circumstances, the vehicle would have to stop for every change of the data to be displayed, which is not practical.
To avoid this problem, the system in the prior art is so designed that the control device judges whether the vehicle is moving or stopped, and controls the VRAMs 110 and 112 in a time sharing manner so as to store different data in each of the VRAMs 110 and 112. The stored data are displayed in the first and/or second displays through the output buffers 111, 113.
Such an aforementioned navigation system in the prior art has the drawbacks that, a large amount of calculation in the control device 104 is required for controlling a plurality of the VRAMs in a time sharing manner so as to store different data in each of them, in order that the data to be displayed in each of the first and second displays can be changed independently. And the amount of the calculation increases according to the number of the VRAMs, therefore, the processing time in the control device is accordingly increased.
An object of the present invention is to eliminate the drawbacks in such a navigation system as in the prior art.
Another object of the present invention is to propose a navigation system in which the data to be displayed in the first display, installed at a position where the driver can not see it, can be changed by passengers other than the driver freely, while the vehicle is moving, without increasing the time required for treating the VRAM according to the number of the displays.
The object is attained by a navigation system according to the present invention, imposing restrictions on the sort of the data to be displayed in the second display while the vehicle is moving.
More precisely, the object is attained by a navigation system, according to the present invention, comprising a first display installed at a position where the driver cannot see it, a second display installed at a position where the driver can see it, a VRAM for storing data to be displayed in each of the displays, a blank signal generating circuit disposed between the VRAM and the second display, and a control device for calculating the data to be displayed in the displays on the basis of data inputted through data inputting means and for storing the result into the VRAM, wherein when the control device detects that the vehicle is moving, the control device controls the blank signal generating circuit so as to restrict the data to be displayed in the second display.
In an embodiment of the navigation system according to the present invention, command indications can be displayed at a part of the screen of the first and second displays, however the display of command indications in the second display is suppressed, while the vehicle is moving. The suppression of the display is performed by an output signal of the blank signal generating circuit.
In an embodiment of the present invention, while the vehicle is moving, only the background color of the screen, for example, black color, is displayed at the part of the screen of the second display where such command indications can be indicated.
Such black background bit signals can be obtained, for example, as a logical product or logical sum of the bit signal of the data from the VRAM and the output of the blank signal generating circuit, when the output of the blank signal generating circuit is constant, for example, LOW or HIGH.